The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs.
For example, tungsten (W) plugs with titanium (Ti) and titanium nitride (TiN) barrier layers have been traditionally used as via plugs in metal interconnect. As the down-scaling continues, via plugs also become smaller and smaller, and such W plugs exhibit increased resistance and become unsuitable in some instances. Improvements in these areas are desired.